As a method for detecting a flaw, such as a crack, which exists in a vicinity of a surface of a metal, an eddy current flaw detection apparatus has been used.
The eddy current flaw detection apparatus is configured such that an eddy current is generated on the surface of an inspection object by applying, to the inspection object, an excitation magnetic field from an excitation coil connected to an AC power source, and such that an induction magnetic field induced by the eddy current is detected by a detection coil.
With the eddy current flaw detection apparatus, a flaw in the inspection object is detected in such a manner that a probe configured by the excitation coil and the detection coil is scanned on the surface of the inspection object, and that a change of the eddy current due to a flaw (crack) which exists in the surface of the inspection object is detected as a change of the induction magnetic field.
Meanwhile, in order to detect a flaw with high sensitivity, it is necessary that the probe be scanned while the probe axis is made to coincide with the normal of the surface of the inspection object.
When the probe inclines during the scanning, the sensitivity of detecting the flaw is reduced, and further, a ghost may be detected.
In order to cope with this, there has been proposed a technique in which, in a test for detecting a flaw in a complicated-shaped surface having a three-dimensional shape change, the probe which is scanned is imaged so that the attitude of the probe is monitored (see, for example, Patent Document 1).